BUG(CoW): also raise for chained assignment for .at / .iat

[jorisvandenbossche]

Noticed while working on #61368. I assume this was an oversight in the original PR #49467 adding those checks. Also added some more explicit tests for all of loc/iloc/at/iat

[mroeschke]

Thanks @jorisvandenbossche

[lumberbot-app]

Owee, I'm MrMeeseeks, Look at me.

There seem to be a conflict, please backport manually. Here are approximate instructions:

1. Checkout backport branch and update it.

git checkout 2.3.x
git pull

2. Cherry pick the first parent branch of the this PR on top of the older branch:

git cherry-pick -x -m1 b84ac0ec647902b9dd0c1bcda790b289f577b617

3. You will likely have some merge/cherry-pick conflict here, fix them and commit:

git commit -am 'Backport PR #62074: BUG(CoW): also raise for chained assignment for .at / .iat'

4. Push to a named branch:

git push YOURFORK 2.3.x:auto-backport-of-pr-62074-on-2.3.x

5. Create a PR against branch 2.3.x, I would have named this PR:

"Backport PR #62074 on branch 2.3.x (BUG(CoW): also raise for chained assignment for .at / .iat)"

And apply the correct labels and milestones.

Congratulations — you did some good work! Hopefully your backport PR will be tested by the continuous integration and merged soon!

Remember to remove the Still Needs Manual Backport label once the PR gets merged.

If these instructions are inaccurate, feel free to suggest an improvement.